But you can always keep them in mind when trying to repair other files. Just for the record, both qpdf and did not work to repair the PDF file automatically. It also tried to fix other problems like a missing xref table, though this will not be relevant to the solution. From mutool clean’s output we see that it has correctly identified that a PDF object is missing the endobj token. Do bear in mind that this may not necessarily always work. In this case, we will use mutool clean which happens to repair the broken object. While we could remedy this by manually adding in the missing keywords, let’s introduce another tool to help fix this automatically: mutool. If we run Didier Stevens’ pdfid on the PDF with pdfid.py VoIP-Research.pdf, we can actually see that there are a mismatched number of obj/ endobjs and stream/ endstreams. This is also the reason why Object 6 was not picked up by pdf-parser or polyfile. As specified on page 36, section 3.2.7 ‘Stream Objects’ of the PDF Reference, Third Edition, this endstream keyword is necessary along with the starting stream keyword as a matching pair. We can see that Objects 3, 4, and 5 have this keyword before endobj. In fact, Object 6 is also lacking the endstream keyword at the end of its Data stream section. It just goes straight to the PDFTrailer denoted by %%EOF. Comparing the FlateDecode Object 3 which displays correctly and the missing FlateDecode Object 6, we notice that Object 6 lacks an EndObject and WhiteSpace3 after its Data section. To figure out what’s going on, let’s look back deeper into the PDF objects in 010 Editor. Interestingly, polyfile also only manages to display 3 of the objects. Polyfile -html voip.html VoIP-Research.pdf Now if we were to run Didier Steven’s pdf-parser, we should be able to list the same objects, decode the streams we need and see what’s in there. Objects 3 and 6 ( 3 0 obj and 6 0 obj), on the other hand, are much larger-sized compressed FlateDecode streams and hence are of greater interest. Running the template shows us that 4 PDF objects were found! Objects 4 and 5 (denoted as 4 0 obj and 5 0 obj) contain streams of length 1 so we can ignore those. Conveniently, 010 Editor already comes with a PDF.bt binary template from its default repository which can parse our malformed PDF file for us. So how do we check out the contents of this PDF? We can use 010 Editor, which is essentially a hex editor on steroids because it comes with binary templates that parses various file format structures and displays them for easy analysis. We are given VoIP-Research.pdf which throws an error message if opened in standard PDF viewers. Feel free to skip to the Summary! Tools Mentioned Thus, I’ll be taking a more long-winded and exploratory path below. In hindsight, while the solution is not difficult and could be pretty short, I found this challenge to be a good opportunity to showcase the different tools that one can usually look to when involved in PDF forensics. I do not have the original challenge title and description with me, although I do remember it was worth the highest possible points for a challenge and First Blood was mine :) I had forgotten what the solution was, but recently I decided to revisit this and figure it out once again after stumbling upon the mess of files I left behind on my hard drive from my original attempts to solve it back then. How to repair damaged PDF file online? Just upload it to our service and get the result in a few seconds.This was a Forensics CTF challenge from Cyberthon 2019’s Online Training. No recognized data from the document will be lost and most of them will be recovered. If an object's relations cannot be identified or recovered, the object will be saved on a separate page at the end of the document (usually the case with embedded graphics). If any relations between objects in a damaged file are missing, the program attempts to restore them. Using advanced recovery algorithms, it identifies various objects in a damaged document. Apart from this, the service supports compressed and uncompressed file types and recovers both types of. Our service allows you to recover *.pdf files of all versions of Adobe Acrobat/Adobe PDF Reader and offers one big HOW to Adobe PDF repair online. After that, it will allow you to preview the recovered document online. Being the best Adobe PDF repair tool online, our service will analyze the contents of the file, the internal data structures of the damaged *.pdf file in an online mode using a number of special algorithms.
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